/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.RetainedWith;
import com.google.j2objc.annotations.Weak;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.function.Function;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import javax.annotation.Nullable;

/**
 * A {@link SetMultimap} whose contents will never change, with many other important properties
 * detailed at {@link ImmutableCollection}.
 *
 * <p>
 * See the Guava User Guide article on
 * <a href= "https://github.com/google/guava/wiki/ImmutableCollectionsExplained"> immutable
 * collections</a>.
 *
 * @author Mike Ward
 * @since 2.0
 */
@GwtCompatible(serializable = true, emulated = true)
public class ImmutableSetMultimap<K, V> extends ImmutableMultimap<K, V> implements SetMultimap<K, V> {
    /**
     * Returns a {@link Collector} that accumulates elements into an {@code ImmutableSetMultimap}
     * whose keys and values are the result of applying the provided mapping functions to the input
     * elements.
     *
     * <p>
     * For streams with {@linkplain java.util.stream#Ordering defined encounter order}, that order
     * is preserved, but entries are {@linkplain ImmutableMultimap#iteration grouped by key}.
     *
     * Example:
     * 
     * <pre>
     * {
     *     &#64;code
     *
     *     static final Multimap<Character, String> FIRST_LETTER_MULTIMAP =
     *             Stream.of("banana", "apple", "carrot", "asparagus", "cherry")
     *                     .collect(toImmutableSetMultimap(str -> str.charAt(0), str -> str.substring(1)));
     *
     *     // is equivalent to
     *
     *     static final Multimap<Character, String> FIRST_LETTER_MULTIMAP =
     *             new ImmutableSetMultimap.Builder<Character, String>().put('b', "anana")
     *                     .putAll('a', "pple", "sparagus").putAll('c', "arrot", "herry").build();
     * }
     * </pre>
     * 
     * @since 21.0
     */
    @Beta
    public static <T, K, V> Collector<T, ?, ImmutableSetMultimap<K, V>> toImmutableSetMultimap(
            Function<? super T, ? extends K> keyFunction, Function<? super T, ? extends V> valueFunction) {
        checkNotNull(keyFunction, "keyFunction");
        checkNotNull(valueFunction, "valueFunction");
        return Collector.of(ImmutableSetMultimap::<K, V>builder,
                (builder, t) -> builder.put(keyFunction.apply(t), valueFunction.apply(t)),
                ImmutableSetMultimap.Builder::combine, ImmutableSetMultimap.Builder::build);
    }

    /**
     * Returns a {@code Collector} accumulating entries into an {@code ImmutableSetMultimap}. Each
     * input element is mapped to a key and a stream of values, each of which are put into the
     * resulting {@code Multimap}, in the encounter order of the stream and the encounter order of
     * the streams of values.
     *
     * <p>
     * Example:
     *
     * <pre>
     * {@code
     * static final ImmutableSetMultimap<Character, Character> FIRST_LETTER_MULTIMAP =
     *     Stream.of("banana", "apple", "carrot", "asparagus", "cherry")
     *         .collect(
     *             flatteningToImmutableSetMultimap(
     *                  str -> str.charAt(0),
     *                  str -> str.substring(1).chars().mapToObj(c -> (char) c));
     *
     * // is equivalent to
     *
     * static final ImmutableSetMultimap<Character, Character> FIRST_LETTER_MULTIMAP =
     *     ImmutableSetMultimap.<Character, Character>builder()
     *         .putAll('b', Arrays.asList('a', 'n', 'a', 'n', 'a'))
     *         .putAll('a', Arrays.asList('p', 'p', 'l', 'e'))
     *         .putAll('c', Arrays.asList('a', 'r', 'r', 'o', 't'))
     *         .putAll('a', Arrays.asList('s', 'p', 'a', 'r', 'a', 'g', 'u', 's'))
     *         .putAll('c', Arrays.asList('h', 'e', 'r', 'r', 'y'))
     *         .build();
     *
     * // after deduplication, the resulting multimap is equivalent to
     *
     * static final ImmutableSetMultimap<Character, Character> FIRST_LETTER_MULTIMAP =
     *     ImmutableSetMultimap.<Character, Character>builder()
     *         .putAll('b', Arrays.asList('a', 'n'))
     *         .putAll('a', Arrays.asList('p', 'l', 'e', 's', 'a', 'r', 'g', 'u'))
     *         .putAll('c', Arrays.asList('a', 'r', 'o', 't', 'h', 'e', 'y'))
     *         .build();
     * }
     * }
     * </pre>
     *
     * @since 21.0
     */
    @Beta
    public static <T, K, V> Collector<T, ?, ImmutableSetMultimap<K, V>> flatteningToImmutableSetMultimap(
            Function<? super T, ? extends K> keyFunction,
            Function<? super T, ? extends Stream<? extends V>> valuesFunction) {
        checkNotNull(keyFunction);
        checkNotNull(valuesFunction);
        return Collectors.collectingAndThen(
                Multimaps.flatteningToMultimap(input -> checkNotNull(keyFunction.apply(input)),
                        input -> valuesFunction.apply(input).peek(Preconditions::checkNotNull),
                        MultimapBuilder.linkedHashKeys().linkedHashSetValues()::<K, V>build),
                ImmutableSetMultimap::copyOf);
    }

    /** Returns the empty multimap. */
    // Casting is safe because the multimap will never hold any elements.
    @SuppressWarnings("unchecked")
    public static <K, V> ImmutableSetMultimap<K, V> of() {
        return (ImmutableSetMultimap<K, V>) EmptyImmutableSetMultimap.INSTANCE;
    }

    /**
     * Returns an immutable multimap containing a single entry.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1) {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        return builder.build();
    }

    /**
     * Returns an immutable multimap containing the given entries, in order. Repeated occurrences of
     * an entry (according to {@link Object#equals}) after the first are ignored.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2) {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        builder.put(k2, v2);
        return builder.build();
    }

    /**
     * Returns an immutable multimap containing the given entries, in order. Repeated occurrences of
     * an entry (according to {@link Object#equals}) after the first are ignored.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        builder.put(k2, v2);
        builder.put(k3, v3);
        return builder.build();
    }

    /**
     * Returns an immutable multimap containing the given entries, in order. Repeated occurrences of
     * an entry (according to {@link Object#equals}) after the first are ignored.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        builder.put(k2, v2);
        builder.put(k3, v3);
        builder.put(k4, v4);
        return builder.build();
    }

    /**
     * Returns an immutable multimap containing the given entries, in order. Repeated occurrences of
     * an entry (according to {@link Object#equals}) after the first are ignored.
     */
    public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
        ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
        builder.put(k1, v1);
        builder.put(k2, v2);
        builder.put(k3, v3);
        builder.put(k4, v4);
        builder.put(k5, v5);
        return builder.build();
    }

    // looking for of() with > 5 entries? Use the builder instead.

    /**
     * Returns a new {@link Builder}.
     */
    public static <K, V> Builder<K, V> builder() {
        return new Builder<K, V>();
    }

    /**
     * A builder for creating immutable {@code SetMultimap} instances, especially
     * {@code public static final} multimaps ("constant multimaps"). Example:
     * 
     * <pre>
     * {
     *     &#64;code
     *
     *     static final Multimap<String, Integer> STRING_TO_INTEGER_MULTIMAP =
     *             new ImmutableSetMultimap.Builder<String, Integer>().put("one", 1).putAll("several", 1, 2, 3)
     *                     .putAll("many", 1, 2, 3, 4, 5).build();
     * }
     * </pre>
     *
     * <p>
     * Builder instances can be reused; it is safe to call {@link #build} multiple times to build
     * multiple multimaps in series. Each multimap contains the key-value mappings in the previously
     * created multimaps.
     *
     * @since 2.0
     */
    public static final class Builder<K, V> extends ImmutableMultimap.Builder<K, V> {
        /**
         * Creates a new builder. The returned builder is equivalent to the builder generated by
         * {@link ImmutableSetMultimap#builder}.
         */
        public Builder() {
            super(MultimapBuilder.linkedHashKeys().linkedHashSetValues().<K, V>build());
        }

        /**
         * Adds a key-value mapping to the built multimap if it is not already present.
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> put(K key, V value) {
            builderMultimap.put(checkNotNull(key), checkNotNull(value));
            return this;
        }

        /**
         * Adds an entry to the built multimap if it is not already present.
         *
         * @since 11.0
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> put(Entry<? extends K, ? extends V> entry) {
            builderMultimap.put(checkNotNull(entry.getKey()), checkNotNull(entry.getValue()));
            return this;
        }

        /**
         * {@inheritDoc}
         *
         * @since 19.0
         */
        @CanIgnoreReturnValue
        @Beta
        @Override
        public Builder<K, V> putAll(Iterable<? extends Entry<? extends K, ? extends V>> entries) {
            super.putAll(entries);
            return this;
        }

        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> putAll(K key, Iterable<? extends V> values) {
            Collection<V> collection = builderMultimap.get(checkNotNull(key));
            for (V value : values) {
                collection.add(checkNotNull(value));
            }
            return this;
        }

        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> putAll(K key, V... values) {
            return putAll(key, Arrays.asList(values));
        }

        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> putAll(Multimap<? extends K, ? extends V> multimap) {
            for (Entry<? extends K, ? extends Collection<? extends V>> entry : multimap.asMap().entrySet()) {
                putAll(entry.getKey(), entry.getValue());
            }
            return this;
        }

        @CanIgnoreReturnValue
        @Override
        Builder<K, V> combine(ImmutableMultimap.Builder<K, V> other) {
            super.combine(other);
            return this;
        }

        /**
         * {@inheritDoc}
         *
         * @since 8.0
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> orderKeysBy(Comparator<? super K> keyComparator) {
            this.keyComparator = checkNotNull(keyComparator);
            return this;
        }

        /**
         * Specifies the ordering of the generated multimap's values for each key.
         *
         * <p>
         * If this method is called, the sets returned by the {@code get()} method of the generated
         * multimap and its {@link Multimap#asMap()} view are {@link ImmutableSortedSet} instances.
         * However, serialization does not preserve that property, though it does maintain the key
         * and value ordering.
         *
         * @since 8.0
         */
        // TODO: Make serialization behavior consistent.
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> orderValuesBy(Comparator<? super V> valueComparator) {
            super.orderValuesBy(valueComparator);
            return this;
        }

        /**
         * Returns a newly-created immutable set multimap.
         */
        @Override
        public ImmutableSetMultimap<K, V> build() {
            if (keyComparator != null) {
                Multimap<K, V> sortedCopy = MultimapBuilder.linkedHashKeys().linkedHashSetValues().<K, V>build();
                List<Map.Entry<K, Collection<V>>> entries = Ordering.from(keyComparator).<K>onKeys()
                        .immutableSortedCopy(builderMultimap.asMap().entrySet());
                for (Map.Entry<K, Collection<V>> entry : entries) {
                    sortedCopy.putAll(entry.getKey(), entry.getValue());
                }
                builderMultimap = sortedCopy;
            }
            return copyOf(builderMultimap, valueComparator);
        }
    }

    /**
     * Returns an immutable set multimap containing the same mappings as {@code multimap}. The
     * generated multimap's key and value orderings correspond to the iteration ordering of the
     * {@code multimap.asMap()} view. Repeated occurrences of an entry in the multimap after the
     * first are ignored.
     *
     * <p>
     * Despite the method name, this method attempts to avoid actually copying the data when it is
     * safe to do so. The exact circumstances under which a copy will or will not be performed are
     * undocumented and subject to change.
     *
     * @throws NullPointerException if any key or value in {@code multimap} is null
     */
    public static <K, V> ImmutableSetMultimap<K, V> copyOf(Multimap<? extends K, ? extends V> multimap) {
        return copyOf(multimap, null);
    }

    private static <K, V> ImmutableSetMultimap<K, V> copyOf(Multimap<? extends K, ? extends V> multimap,
            Comparator<? super V> valueComparator) {
        checkNotNull(multimap); // eager for GWT
        if (multimap.isEmpty() && valueComparator == null) {
            return of();
        }

        if (multimap instanceof ImmutableSetMultimap) {
            @SuppressWarnings("unchecked") // safe since multimap is not writable
            ImmutableSetMultimap<K, V> kvMultimap = (ImmutableSetMultimap<K, V>) multimap;
            if (!kvMultimap.isPartialView()) {
                return kvMultimap;
            }
        }

        ImmutableMap.Builder<K, ImmutableSet<V>> builder =
                new ImmutableMap.Builder<K, ImmutableSet<V>>(multimap.asMap().size());
        int size = 0;

        for (Entry<? extends K, ? extends Collection<? extends V>> entry : multimap.asMap().entrySet()) {
            K key = entry.getKey();
            Collection<? extends V> values = entry.getValue();
            ImmutableSet<V> set = valueSet(valueComparator, values);
            if (!set.isEmpty()) {
                builder.put(key, set);
                size += set.size();
            }
        }

        return new ImmutableSetMultimap<K, V>(builder.build(), size, valueComparator);
    }

    /**
     * Returns an immutable multimap containing the specified entries. The returned multimap
     * iterates over keys in the order they were first encountered in the input, and the values for
     * each key are iterated in the order they were encountered. If two values for the same key are
     * {@linkplain Object#equals equal}, the first value encountered is used.
     *
     * @throws NullPointerException if any key, value, or entry is null
     * @since 19.0
     */
    @Beta
    public static <K, V> ImmutableSetMultimap<K, V> copyOf(
            Iterable<? extends Entry<? extends K, ? extends V>> entries) {
        return new Builder<K, V>().putAll(entries).build();
    }

    /**
     * Returned by get() when a missing key is provided. Also holds the comparator, if any, used for
     * values.
     */
    private final transient ImmutableSet<V> emptySet;

    ImmutableSetMultimap(ImmutableMap<K, ImmutableSet<V>> map, int size,
            @Nullable Comparator<? super V> valueComparator) {
        super(map, size);
        this.emptySet = emptySet(valueComparator);
    }

    // views

    /**
     * Returns an immutable set of the values for the given key. If no mappings in the multimap have
     * the provided key, an empty immutable set is returned. The values are in the same order as the
     * parameters used to build this multimap.
     */
    @Override
    public ImmutableSet<V> get(@Nullable K key) {
        // This cast is safe as its type is known in constructor.
        ImmutableSet<V> set = (ImmutableSet<V>) map.get(key);
        return MoreObjects.firstNonNull(set, emptySet);
    }

    @LazyInit
    @RetainedWith
    private transient ImmutableSetMultimap<V, K> inverse;

    /**
     * {@inheritDoc}
     *
     * <p>
     * Because an inverse of a set multimap cannot contain multiple pairs with the same key and
     * value, this method returns an {@code ImmutableSetMultimap} rather than the
     * {@code ImmutableMultimap} specified in the {@code
     * ImmutableMultimap} class.
     *
     * @since 11.0
     */
    public ImmutableSetMultimap<V, K> inverse() {
        ImmutableSetMultimap<V, K> result = inverse;
        return (result == null) ? (inverse = invert()) : result;
    }

    private ImmutableSetMultimap<V, K> invert() {
        Builder<V, K> builder = builder();
        for (Entry<K, V> entry : entries()) {
            builder.put(entry.getValue(), entry.getKey());
        }
        ImmutableSetMultimap<V, K> invertedMultimap = builder.build();
        invertedMultimap.inverse = this;
        return invertedMultimap;
    }

    /**
     * Guaranteed to throw an exception and leave the multimap unmodified.
     *
     * @throws UnsupportedOperationException always
     * @deprecated Unsupported operation.
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    public ImmutableSet<V> removeAll(Object key) {
        throw new UnsupportedOperationException();
    }

    /**
     * Guaranteed to throw an exception and leave the multimap unmodified.
     *
     * @throws UnsupportedOperationException always
     * @deprecated Unsupported operation.
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    public ImmutableSet<V> replaceValues(K key, Iterable<? extends V> values) {
        throw new UnsupportedOperationException();
    }

    private transient ImmutableSet<Entry<K, V>> entries;

    /**
     * Returns an immutable collection of all key-value pairs in the multimap. Its iterator
     * traverses the values for the first key, the values for the second key, and so on.
     */
    @Override
    public ImmutableSet<Entry<K, V>> entries() {
        ImmutableSet<Entry<K, V>> result = entries;
        return result == null ? (entries = new EntrySet<K, V>(this)) : result;
    }

    private static final class EntrySet<K, V> extends ImmutableSet<Entry<K, V>> {
        @Weak
        private final transient ImmutableSetMultimap<K, V> multimap;

        EntrySet(ImmutableSetMultimap<K, V> multimap) {
            this.multimap = multimap;
        }

        @Override
        public boolean contains(@Nullable Object object) {
            if (object instanceof Entry) {
                Entry<?, ?> entry = (Entry<?, ?>) object;
                return multimap.containsEntry(entry.getKey(), entry.getValue());
            }
            return false;
        }

        @Override
        public int size() {
            return multimap.size();
        }

        @Override
        public UnmodifiableIterator<Entry<K, V>> iterator() {
            return multimap.entryIterator();
        }

        @Override
        boolean isPartialView() {
            return false;
        }
    }

    private static <V> ImmutableSet<V> valueSet(@Nullable Comparator<? super V> valueComparator,
            Collection<? extends V> values) {
        return (valueComparator == null) ? ImmutableSet.copyOf(values)
                : ImmutableSortedSet.copyOf(valueComparator, values);
    }

    private static <V> ImmutableSet<V> emptySet(@Nullable Comparator<? super V> valueComparator) {
        return (valueComparator == null) ? ImmutableSet.<V>of() : ImmutableSortedSet.<V>emptySet(valueComparator);
    }

    private static <V> ImmutableSet.Builder<V> valuesBuilder(@Nullable Comparator<? super V> valueComparator) {
        return (valueComparator == null) ? new ImmutableSet.Builder<V>()
                : new ImmutableSortedSet.Builder<V>(valueComparator);
    }

    /**
     * @serialData number of distinct keys, and then for each distinct key: the key, the number of
     *             values for that key, and the key's values
     */
    @GwtIncompatible // java.io.ObjectOutputStream
    private void writeObject(ObjectOutputStream stream) throws IOException {
        stream.defaultWriteObject();
        stream.writeObject(valueComparator());
        Serialization.writeMultimap(this, stream);
    }

    @Nullable
    Comparator<? super V> valueComparator() {
        return emptySet instanceof ImmutableSortedSet ? ((ImmutableSortedSet<V>) emptySet).comparator() : null;
    }

    @GwtIncompatible // java.io.ObjectInputStream
    // Serialization type safety is at the caller's mercy.
    @SuppressWarnings("unchecked")
    private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
        stream.defaultReadObject();
        Comparator<Object> valueComparator = (Comparator<Object>) stream.readObject();
        int keyCount = stream.readInt();
        if (keyCount < 0) {
            throw new InvalidObjectException("Invalid key count " + keyCount);
        }
        ImmutableMap.Builder<Object, ImmutableSet<Object>> builder = ImmutableMap.builder();
        int tmpSize = 0;

        for (int i = 0; i < keyCount; i++) {
            Object key = stream.readObject();
            int valueCount = stream.readInt();
            if (valueCount <= 0) {
                throw new InvalidObjectException("Invalid value count " + valueCount);
            }

            ImmutableSet.Builder<Object> valuesBuilder = valuesBuilder(valueComparator);
            for (int j = 0; j < valueCount; j++) {
                valuesBuilder.add(stream.readObject());
            }
            ImmutableSet<Object> valueSet = valuesBuilder.build();
            if (valueSet.size() != valueCount) {
                throw new InvalidObjectException("Duplicate key-value pairs exist for key " + key);
            }
            builder.put(key, valueSet);
            tmpSize += valueCount;
        }

        ImmutableMap<Object, ImmutableSet<Object>> tmpMap;
        try {
            tmpMap = builder.build();
        } catch (IllegalArgumentException e) {
            throw (InvalidObjectException) new InvalidObjectException(e.getMessage()).initCause(e);
        }

        FieldSettersHolder.MAP_FIELD_SETTER.set(this, tmpMap);
        FieldSettersHolder.SIZE_FIELD_SETTER.set(this, tmpSize);
        FieldSettersHolder.EMPTY_SET_FIELD_SETTER.set(this, emptySet(valueComparator));
    }

    @GwtIncompatible // not needed in emulated source.
    private static final long serialVersionUID = 0;
}
